China's quake: Why did so many schools collapse?
Earthquake experts say the collapsed schools may be a sign of poor construction despite adequate building codes.
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"You can buy the building inspector," he says, but "you can't buy off the earthquake."
China has a history of massive earthquakes. About 200 of its cities with a population of over a million are located at risk of magnitude 7 earthquake.
"In this case, where the earthquake occurred, there are a magnitude 4 earthquakes every couple of months," says Lupei Zhu, an associate professor of geophysics, at St. Louis University in Missouri, and a former employee of the China Earthquake Administration, which oversees public awareness and the collection of seismic data for the country.
Bill Murphy, an engineering geologist at the University of Leeds in England, notes that magnitude of the quake is only one measure. "It's not so much the magnitude, but the amount of shaking," he says. "Some of these aftershocks [in Sichuan] have been earthquakes in their own right. That might cause some additional buildings to collapse, especially those that have been weakened by the main earthquake."
"The seismic code for the area substantially underestimated the earthquake strength," said Hong Hao. He said that China's earthquake regulations class this province as equivalent to a 7 on the Mercalli intensity scale, which uses historical information to assess risk of damage from earthquakes. That means there's a 10 percent risk of an earthquake occurring every 50 years of an intensity that would cause negligible damaged. Monday's quake was a 10 or 11 on the Mercalli scale.
Xinhua said more than 12,000 had died in Sichuan province alone, but the total number of casualties remained uncertain. In a massive government relief operation, some 20,000 soldiers and police have arrived in the area, with 30,000 more on the way.
• Material from the Associated Press was used in this report.